A roller coaster is a thrilling amusement park ride with passenger cars that race along a twisting metal track, climbing steep hills and plunging down sharp drops at high speeds. The cars don't have engines; instead, they're pulled to the top of the first big hill, then gravity and momentum do the rest of the work, sending riders zooming through loops, corkscrews, and sudden turns.

The first roller coasters appeared in the 1800s and were much tamer than today's versions. Modern roller coasters can reach speeds over 100 miles per hour and feature inversions that flip riders completely upside down. Some hang riders beneath the track with their legs dangling. Others launch forward like a rocket instead of climbing a first hill. Engineers spend years designing each coaster, calculating every angle and curve to create maximum excitement while keeping riders safe.

People also use roller coaster to describe any experience with dramatic ups and downs. A basketball game where the score keeps swinging back and forth might be called a roller coaster. Someone describing a difficult week might say, “It's been a real roller coaster,” meaning they experienced wild swings between good moments and bad ones, like the thrilling peaks and stomach-dropping valleys of the ride itself.